Annealing furnace



Feb. 7, 1939. u. HUFF ANNEALING FURNACE Filed July 14, 1957 3Sheets-Sheet l I .ZI.

INVENTOR. dwmd J fii f/ BY 5 Maw/4m ATTORNEYS.

Feh 7fl39 E. HUFF "2,146,432

ANNEALING FURNACE Filed July 14, 1957 s Sheets-Sheet 2 INVEN TOR.

BY @447 Md MW ATTORNEYS.

Feb. 7, 1939. E. l. HUFF 2,146,432

I ANNEALING FURNACE Fil ed Ju'ly14, 1957 :5 Sheets-Sheet s X g D IN VENTOR. D zz l2 62am! W ATTORNEYS.

Patented Feb. 7, 1939 UNITED STATES ANNEALIN G FURNACE Edward I. Hufl',Reifl'ton, Pa., assignor to Hull Equipment Company, a corporation ofPennsylvanla Application July 14, 1937, Serial No. 153,585

This invention relates to the annealing of metal, and consists in anannealing furnace peculiarly adapted to the annealing of rolled steelstrip. -Its objects are economy in structure and in operating cost, andexcellence of product.

The invention is illustrated in the accompanying drawings. Fig. I is aview of a furnace of the invention in vertical section; Figs. II and IIIare views in horizontal section, on the planes indicated at IIII andIII-III, Fig. I. Figs. IV and V are views, in vertical section and inplan from beneath, of the hood alone that forms part of the furnaceassembly; Figs. VI and VII are views in plan from above and in verticalsection of the pan that in the assembly rests upon the furnace hearthand immediately receives and carries the hood. Fig. VIII is afragmentary view, corresponding to Fig. I, that illustrates analternative arrangement in the matter of heat source. Fig. IX is a viewthat corresponds to Fig. III, of a furnace of more elaborate structure.In this drawing, to the left of the middle line, the hearth appears inplan, the outer walls of the furnace (which are removable) not being inplace.

Conflning attention first to the simpler structure of Figs. I-VII, thefurnace is of muflie type and includes an outer heat-insulating wall Iand an inner heat-conducting mufiie'2. The muflie is thin-walled andmade of metal. It is spaced from the outer wall, and the space C betweenis the combustion chamber, within which heataffording. flame may bedeveloped. The space M within the muffie is the muffle chamber, withinwhich the material to be treated is enclosed.

In modern practice ingots and billets of steel are reduced in continuousoperation to highly attenuated strip of great and indefinite length.

- On completion of the rolling operation the strip is in the form of acompact spiral coil that may be handled as a unit, and in such form itmay be, and it is desirable that it should be, subjected to therequisite annealing operation. The primary object of my invention is toaccomplish the annealing of such a coil of strip steel, and toaccomplish it in such manner that the quality of the annealed articleshall be substantially uniform, throughout its extent.

'I'heoperation of annealing consists in heating the material to a peaktemperature and cooling it again; and, while rate of heating, peaktemperature, time at peak, and rate of cooling must (in order to attaindesired results) conform to a certain standard, there is a margin oftolerance; and if throughout all its extent the strip in its treatmentbe brought within such margin, the product will be of uniform qualitythroughout. In the operation of the furnace of my invention the materialis so brought Within the margin of tolerance, and the annealed productis of uniform and standard quality.

The muille 2 is of usual structure in that it consists of integral andimperforate side and top walls, is open at. the bottom, and is adaptedto rest upon a horizontal base. It is unique,- in that it is of annularshape. It is shown in vertical section in Fig. IV, in plan from beneathin 1 Fig. V, and in plan from above in Fig. III; and it is shown inassembly in Fig. I, and there it is shown to contain and inclose thematerial S tobev treated. The furnace charge is here shown to consist ofthree superposed coils S of rolled strip. The proportioning of themuflie in height to the strip in breadth, and the piling of the coils ofstrip one upon another within the muille chamber, will be understood tobe matters that admit of variation; and it will be understood that inthese particulars the showing is exemplary merely. Ordinarily, rolledsheet rests flat within the annealing furnace; in the furnace of myinvention it will be observed that the strip when under treatment standsupon edge.

The mufile in the assembly rests, as is usual, upon a pan 3, and the panin turn lies horizontally upon the hearth 4 of the furnace. The pan isdoubly flanged both at its inner and outer margins, and the lower edgeof the hood engages the bottom of the pan between these pairs offlanges, and luting L is applied, as shown in Figs. I and II. An annularblock 5, arranged within the doubly flanged margins of pan 3, may affordsupport for an annular stool 6, upon which the furnace charge Simmediately rests.

The all-inclosing outer-wall of the furnace is, as has been said, formedesentially of heat-insulating material; and preferably it consists of abox-like structure, otherwise closed, but open at the bottom, applicableto and removable from the stationary and horizontally extending hearth4. The walls of insulating material are built within a supporting shellof metal II, and this shell of metal, extended downwardly, may in theassembly enter a channel formed in the hearth for its reception, andluting may there be provided, as indicated at L Fig. I. In Fig.1 theframe of the box-like structure is shown to be provided with a perforatelug l2, for the attachment to it of raising and lowering mechanism.

The cross-sectional form of the box that forms the outer furnace wall isnot of controlling importance. The square form shown in Fig. III isconvenient.

When the movable parts of the furnace are assembled, the'outer furnacechamber includes the space 0 that surrounds the muiiie and this space iscontinuous over the top of the mui'lie with the central space D withinthe annulus of the muiile. The invention is achieved in effectingcirculating of streams of hot gas upward over the outer wall of themuiile inward over the top, and downward through the central spacewithin the annulus. This commonly is done by organizing, with thefurnace assembly described, a plurality of bumers I that extend throughthe outer walls I and that deliver their flames at the base of theouter, muiiie-surrounding space C, and a flue 8 for the products ofcombustion that leads from the inner central space D through the furnacehearth. The tongues of flame that spring at the base of the mui'fle andat the outer periphery' thereof rise within space C, stream over themuille, and converge and form a stream that flows downward through thecentral space D to the flue 8. The lines of flow are indicated in Fig. Iby arrowpoints. Preferably the line of direction in which the burners 1project their flames are approximately tangent to the cylindrical outersurface of the muille 2. The outer wall I being of square cross-section,the number of burners 1 is conveniently four-one in each of the fourwalls.

The pan 3, flanged as has been described, may have its innermost flangeextended downwardly at II, as well as upwardly, thus facilitatingassembly, and rendering the assembly more secure.

It will be perceived that the tongues of flame swirl as they rise aroundthe outer walls of the mume, and that they merge in the stream thatflows downward through the space D toward the exit. The flame is hottestwhere it is most widely extended-over the outer surface of the muille;and as in its progress the temperature declines the stream isconcentrated and flows in a passageway whose walls are wholly ofheat-conducting material, carrying heat to the muille chamber, and moreimmediately to the inner portion of the coils of material within thechamber. Thus increase in heat-receptivity, or (more accuratelyspeaking) the more complete taking up by the material of the heat as itis released, affords compensation for the diminution in rate of heatrelease; and in consequence the coils of material within the muillechamber are heated at approximately equal rate through exterior andinterior surfaces, and are brought with substantial uniformity and withspeed to the desired peak.

Further refinement is found in prolonging the flue 8 in a spiral beneaththe floor of the furnace (cf. Figs. I and II). This spiral at its outerend communicates with a duct 9 that leads to a stack or otherdraft-maintaining structure. Heat loss through a furnace floor is in anycase at a minimum; but by the provision of a flue 8 beneath the floor Iachieve an actual input of heat, even through the floor, into thefurnace chamber; and so, subjecting the coiled material peripherallycentrally above and below to a condition of heat intake, I provide forthe heating of the material with uniformity well within the margin oftolerance of which I have spoken.

The method of operation is essentially the method that is commonlypracticed in furnaces of such sort. The pan 3 is brought to positionupon hearth I; the block 5 is placed in the pan; the stool 8 is set onthe block; and the furnace charge 8 is placed on the stool. The muffle 2is then lowered to place, and when in place, resting at its edges in pan3, the luting L is'attended to.

.That is to say, the munle may be lowered and sunk into previouslyprepared beds of luting; or the luting may be applied wholly or in partafter the muilie has been lowered to place. The outer boxlike furnacepart then is applied and brought to position on the hearth; and theluting 1.. is attended to. Connections are made for carrying fuel to theburners I; and, all being made ready. fuel is admitted and the burnerslighted. The flames stream through the furnace and eflect the heating inthe manner described. It will be understood that the supply of fuel andthe conditions of draft may be regulated in well-known manner, to bringthe material at desired speed to the desired peak temperature. The peakhaving been gained, and the peak temperature maintained for the desiredlength of time, cooling again at desired rate may be effected byradiation, accelerated if desired by circulation of air through the lineof flame-flow, as the art well knows.

Indeed, in my structure, a counter circulation of cooling air isemployed with advantage. That is to say, when the peak temperature hasbeen gained and maintained for the desired length of time, the outerbox-like furnace part is lifted from the hearth; the outer walls of themuflie 2 give up heat immediately to the outer air, and

hearth of the furnace is cooled with the walls of a the muflie, and amore uniform and gradual cooling of the charge is obtained.

I have described an installation in which the heating flame is projecteddirectly into the outer chamber and caused to stream over the outersurface of the muille. The invention in broader aspect admits manifestlyof indirect heating. It is essential to the invention that streams ofheated gas flow in the outer chamber from the base of the muflle upwardover the outer wall of the annular muffle, inward over the top wall, anddownward over the inner wall; and, while under ordinary and usualconditions those streams of gas will be heated by the combustion oftheir component substances, they manifestly may be heated by causingthem to flow over heated bodies. This is indicated in Fig. VIII, where abank of combustion tubes 10 is shown, arranged at the base of the outerchamber C. From the fines in the hearth of the furnace, passages 'II (ofwhich there may be a suitable number, of suitable size) open into thebottom of the space C between the outer wall of the furnace and themunie 2. The tubes 10 being hot, it is manifest that the body of airwithin the furnace will circulate. Streams of air will flow over thetubes 10 and will be heated; the heated air will flow over the walls ofthe muflle in the course indicated by the arrow points in Fig. I, andwill impart heat. in the manner already described; and, upon descendingthrough the inner space D and entering the underfloor flues 8, the airflows through passages ll into the bottom of outer space C. Thus, heatedair is continuously circulated within the furnace, to heat the charge todesired temperature.

The furnace of Fig. IX will be understood with very little furtherexplanation. In this case the outer furnace walls l2 are so enlarged asto receive an extended muiile 22; within which may 7 be arranged amultiplicity of such units as the single unit shown in the other figuresof the drawings. The extended mullie 22 is but a plurality of mufiles 2merged into'one, and provided with a plurality of passageways D thatseverally are continued in flues 8 in the hearth. In such case there isa plurality of blocks carrying each a stool, and each stool carrying oneor more coils, as has already been explained. A single muiile 22overarches and incloses all the pans with their bur- .den's. There is asingle external flame space into which the combustible mixture isdelivered, and within which the flame is developed. The mufiie is soparticularly shaped that in the assembly there is a passageway Ddescending through each stool with its burden of coiled material. Withthis modification in organization, the operation is essentially thatalready described. Ihe flames spring at the base of the muffle on itsouter side and rise around the mufile, to flow over its top and descendthrough the passageways within the coils to the multiplicity of fines inthe hearth. These dues are here shown to lead to headers 80, and fromthe headers flues 8| rise in the side walls l2. These flues 8|, sosituated, tend to reduce heat loss through the walls l2.

The furnace is of simple construction, easy to be operated, readilyresponsive to the demands of the metallurgist, and affords aheat supplyso distributed as to afford, with material shaped and disposed asspecified, a product of uniform quality.

I claim as my invention:

1. An annealing furnace for an annular body including a hearth in whichis formed a spiral flue with central intake and peripheral delivery, anouter inclosing furnace wall of heat-insulating material removably borneby the hearth, an inner inufiie of heat-conducting material and ofannular shape and consisting of continuous and imperforate inner andouter side walls and a top wall continuous with the inner-and outer sidewalls, and open at the bottom, removably-borne by the hearth within theouter wall and when in '5 place spaced from the outer wall, the centreof the annulus in open communication with the spiral flue at the intakeend, and adapted when in place to enclose a charge of material restingon the hearth and a plurality of burners extendin; through the outerfurnace wall at the base thereof and at intervals around thecircumferential extent of the wall and adapted when the parts areassembled to deliver flamesto the space between the outer furnace walland the mufile wall, whereby such flames springing at the base of themufile and at the outer periphery thereof flow upward over the surfaceof the muflle and converge and descend through the centre of the annulusand thence to the spiral fine in the hearth.

2. An annealing furnace for an annular body including a hearth in whichis formed a spiral fiue with central intake and peripheral delivery, anouter inclosing furnace wall of heat-insulating material removably borneby the hearth, an inner inclosing muflie wall of heat-conductingmaterial and of annular shape and consisting of continuous andimperfcrate inner and outer side walls and a top wall continuous withthe inner and outer side walls, and open at the bottom, removably borneby the hearth within the outer wall and when in place spaced from theouter wall, the centre of the annulus in open communication with thespiral fine at the intake end, and adapted when in place to enclose acharge of material resting on the hearth, and a plurality of burnersextending through the outer furnace wall at the base thereof and atintervals around the circum ferential extent of the furnace and intangential direction with respect to the said muffle wall of annularshape and adapted when the parts are assembled to deliver flames to thespace between the outer furnace wall and the muflle wall, whereby suchflames springing at the base of the mufile and at the periphery thereofflow upward over the surface of the muflie and converge and descendthrough the centre of the annulus and thence to-the spiral flue in thehearth.

EDWARD I. HUFF.

